1. Field of the Invention
The present invention relates to a rotary electric machine with a rotor, such as an electric motor or a power generator. Particularly, it relates to a permanent magnet-embedded type rotary electric machine in which at least one permanent magnet is embedded in a rotor.
2. Description of the Background Art
In a permanent magnet-embedded type rotary electric machine, cogging torque occurs when a rotor is rotated even in a non-excited state. The cogging torque should be minimized because the cogging torque is a disturbance in the control of the rotary electric machine. One of measures for reducing the cogging torque is a measure in which an oblique skew is applied to a stator or a stepwise skew is applied to a rotor. However, when this measure is taken, there is a problem that the number of manufacturing steps increases. As a technique for reducing cogging torque without applying any skew to a stator or a rotor, there is, for example, a technique disclosed in JP-A-2004-343861. According to the technique in JP-A-2004-343861, a range through which magnetic flux can pass is limited by slits provided in end portions of each magnetic pole of a rotor, and the width of the range is defined based on the pitch of slots for stator windings so as to reduce cogging torque.
The aforementioned background-art permanent magnet-embedded type rotary electric machine has a problem that cogging torque may fluctuate unstably when the dimensions of the slit for limiting the width of the range through which magnetic flux can pass differ from its design dimensions due to the influence of a manufacturing error.